17963 maximum boost exceeded? intermitent boost problem??

hey all, been having a boost issue! car idles great, pulls great in first and second occasionally in third and never holds boost in the later gears? its hitting soft limp i think, umplugged the maf no change, unplugged the n75 no change, guess the ecu is cutting fuel aswell!!

scanned her after deleting the codes and going for a drive, got the one in the title and the weak maf signal one... so ive ordered the maf sensor and now im puzzled as i replaced the n75 today?

if it were a leak would it be in every gear???

also i suspected the valve between the rocker cover and turbo intake pipe so i removed it and it was full of gunk, figured i'd blank the tip side and go for a spin, it wasnt perfect but ran alot better and held boost in third and fourth pretty well!? i soaked it in wd40 and refitted but havent had time for a drive yet?

lastly the new n75 is black and the old one is brown, the brown one was fitted with the wireing connector facing the engine and the longer horizontal spout entering the tip, to have the new n75 facing the same way the shorter spout enters the turbo pipe...? is it the wright way round?-)

ive had this car a week by the way and knew it had a few issues, i like a challenge but this engine is so complicated...

really just trying to give as much info as possible encase anyone else has had this problem?

oh could it be a cheap map? its stage 1 by a back street garage! n247 bypass, forge dv, pipercross panel filter,

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tbh... most likely this.... but... without checking with data logging its gonna be difficult to determine... if you had a map that was known to be good then its normally a hardware issue such as a split pipe etc but difficult to say without logs..

You say you unplugged the N75? I assume electrically? if electrically disconnected then you shouldn't see more than actuator pressure

Simple test is to join the pipe from the actuator to the pipe coming off the charge pipe (or run a suitable length and ID of pipe)... this will bypass the N75 and run actuator pressure only... if you are still seeing more than 0.5bar then its the actuator or turbo

You have the N75 the wrong way around... the brown one is a J-Valve... hideous pikey mode that typically causes limp mode due to its ability to spike the boost... anyhoo... the long outlet goes into the TIP, boost goes in the bottom and the short one opposite to the long one to the actuator...

great your life savers i'll try this in the morning... this is one break through!-)

still think theres leaks aswell though as ive been reading about negative boost on idle with alot of people saying you should be -20 psi at idle, im at -.7 bar so about 10psi... is this a full proof method?

so basically the guys on here telling people they have airleaks if they arnt at 20psi are giving out false info? im assuming your beast is pretty much leak free ya? cheers mate i'll update in the morning dude.

You have the N75 the wrong way around... the brown one is a J-Valve... hideous pikey mode that typically causes limp mode due to its ability to spike the boost... anyhoo... the long outlet goes into the TIP, boost goes in the bottom and the short one opposite to the long one to the actuator...

Soz, skim read fail... this will sort your boost issue out for sure

<tuffty/>

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Although my thoughts about the N75 worked out to sound right, my intentions were completely WRONG.
I keep thinking the actuator needs boost pressure to keep it closed, when it actually uses the pressure to open it. Geeez I need to write this down somewhere, like on the back of the toilet door

uuurgh not fixed! right, ran fine for a good few miles then soft limp activated again, this time 2 codes... maximum boost pressure exceeded and now high maf signal!? the connector for the maf has seen better days and doesnt clip down so i wiped the codes then cable tied it down nice and tight, went for a spin giving it full beans at every opportunity. she seemed fine for 15 or so miles then on the way back up the steep hill where i live, you've guessed it same codes and soft limp, i wiped the codes a little stutter from the engine then a few minutes home on full boost!???

just like to note both the n75 and maf are cheap ebay jobbies a be it brand new... as its nearly fixed my problem should i now buy audi parts (n75 and maf) and get a new connector for the maf?

right things are getting better but its still there, theres a bosch maf and thats removed the maf code, a oem n75 has helped smooth out the power delivery further, this weekend i replaced all the thin vacume hoses with blue silicone ones and proper bolt clips, also done both the hoses of the n75... the more i mess with the less frequent i hit overboost soft limp but its still there...

one thing i have noticed is the dv i was told was forge is actually a 29.99 ebay jobbie!!! im bidding on a forge split r with blanking plate atm, would a **** recirc dv cause overboost?

better results have been seen with the OEM DV (and a hell of a lot cheaper!)

I too had the same issues as you, turned out my N75 was knackered - ordered an OEM one off eBay (germanautospares i think their name was) and also did the OEM DV and N249 bypass at the same time, haven't had the error code since - completely transformed the car as the N75 was knackered when I brought it I just thought that's how an S3 is meant to be until I read the fault codes.

right things are getting better but its still there, theres a bosch maf and thats removed the maf code, a oem n75 has helped smooth out the power delivery further, this weekend i replaced all the thin vacume hoses with blue silicone ones and proper bolt clips, also done both the hoses of the n75... the more i mess with the less frequent i hit overboost soft limp but its still there...

one thing i have noticed is the dv i was told was forge is actually a 29.99 ebay jobbie!!! im bidding on a forge split r with blanking plate atm, would a **** recirc dv cause overboost?

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Don't buy a bloody Split-r!!!... they leak worse than your ebay ****... buy a pucker 007p (new ones have a revised leak free piston) or just stick to OE as they hold 30psi no probs without leaking..

Overboost is over boost... leaking valve will leak boost.. so no, I doubt your cheap valve is the reason for the overboost... you need to log with VCDS to establish whats actually going on assuming you have already checked the pipework going to the N75 valve (and its not the brown pikey J-valve of course)

Unplug the N75 electrically and see if the boost sits happily at actuator pressure... if you see more than 0.5bar of boost then its plausible you have split pipes... the normal suspect is the one coming off the charge pipe which splits at the outlet... this provides the boost feed to the N75 for actuator control

ok more sound advise, i will do mate... have to get my head round this logging stuff, guess this works with the free vcds? as i wrote above mate ive changed the n75 pipework and small vac hoses around the inlet mani for silicone ones... will try the unplugged n75 which yes is an oem one now!-)

dont make sense man?-0 if a leaking valve will leak boost why would you doubt it? ive ordered a new oem valve now to eliminate that anyways...

i will try the unplugged n75 in a bit

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You are getting an over boost fault code... this is when the boost level exceeds 200mbar of the requested boost... leaky valves leak boost... this reduces overall boost... your over boost issue is due to a component failing to control boost not due to boost leaking..

ok, so if a leak in the n75 pipe work can cause the n75 to creat overboost why cant a leak in the dv, its all linked right? just trying to clarify it in my head, not questioning you dude...

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A leak in the N75 valve pipework means there is potentially no air pressure going to the actuator and therefore nothing to 'control' boost... a leaking DV is in the main charge air tract and will just leak air back to the inlet rather than it ending up in the engine... this will reduce power... so no... not actually linked....

For what its worth boost leaks from pipes tend to make less difference than you think... you tend to lose more at the top end as boost will drop off sooner and won't hold as long... having no pressure going to the actuator is a far more serious affair..

right just back, n75 unplugged it holds 0.5bar until 4000rpm then gradually rises with the revs to about 1.2 bar by the redline... without soft limp being hit then aswell... (hits it alot less than before i done the silicone hose)

Hummm... you have boost creep then... has the turbo been replaced at all that you are aware of? Have seen std K04's do this in the past though... could be an iffy actuator... 0.5bar is normal actuator pressure... 1.2bar isn't though... if the actuator is iffy then could explain the overboost... the N75 not being able to open the actuator enough to control the boost... logging in VCDS will give an idea of what the ECU is seeing...

the turbo im told was replaced in 2011 with a genuine one of ebay, it never smokes... all i have in the history is a screen shot of the ebay page...?

the bosch n75 wasnt brand new but came off ebay, could it still be the culprit? maybe?

also how do i do this logging stuff?

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A genuine one from eBay?... hummm... if its an actual eBay one (chinese copy) then this would explain the boost creep and the only fix is to remove the turbo and get the wastegate aperture ported... copy hotsides are renowned for this issue... have seen them creep to 20psi before...

Need to verify if its an actual genuine turbo... should have a little blue plate pop riveted to the compressor housing...

I am having something similar. In 6th gear around 130-140 Kph I am losing turbo boost. It's like I'd have a minimal but can't feel any real power. If I stopped the car then restart it, there is still no boost but after a few minutes it's back!
Where to start? (ASZ, 8L, PD TDI 2003). Thanks!

Oh, a small to add, I have had around 80-100 fault codes since I bought the car (obviously something st*pid since it says ie.: quattro failure which would be great if I had a quattro but indeed I am not having one, it's FWD). The car was 'great' until yesterday, now I got the boost issue.

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